# Re-sign part URLs for an upload already in flight
Source: https://docs.file.ai/api-reference/uploads/re-sign-part-urls-for-an-upload-already-in-flight

> Return freshly signed URLs for specific parts of a multipart upload that is still in progress, each valid for another 900 seconds.

post /prod/v1/files/upload/multipart/urls/refresh

Return freshly signed URLs for specific parts of a multipart upload that is still in progress, each valid for another 900 seconds.

This is what makes a long bulk transfer work. Part URLs are deliberately short-lived, so a
30-file transfer will outlive the URLs it started with; ask for the parts still outstanding
and carry on.

Nothing about the upload changes. Parts already uploaded under earlier URLs stay uploaded,
the upload id is unchanged, and completion still expects the full part list.

The input should contain:
- `id`: the ID from the multipart upload initiation
- `key`: the S3 key from the multipart upload initiation
- `partNumbers`: the parts to re-sign, 1-based and within the upload's `totalParts`

An `id`/`key` pair that does not belong to your API key's account returns 404, the same as
one that never existed.